1. Field of the Invention
The invention generally relates to wireless communication systems, and more particularly, to establishing connectivity in a cellular communication system.
2. Description of the Related Art
Wireless communication systems support a sleep mode to minimize battery power consumption of user equipment (UE), such as a mobile terminal. In sleep mode, the mobile terminal performs little or no activity, and does not transmit/receive traffic data. Therefore, the mobile terminal in sleep mode only consumes a small amount of radio link resources, if any. Consequently, a large number of users can simultaneously be supported in the system.
A mobile terminal can terminate sleep mode and connect to a Radio Access Network (RAN) of base stations (otherwise known as “Node B”s according to the 3GPP protocol) in two ways. If traffic needs to be transmitted from the mobile terminal, the mobile terminal may terminate the sleep mode by requesting a connection to the network. This is denoted a “mobile terminal initiated (originated) connection.” Otherwise, the network may request the mobile terminal to make a connection to the network. This is denoted a “network-initiated connection”. The procedure used for waking up the mobile terminal from the sleep mode in “network-initiated connection” employs paging.
Paging involves waking up the mobile terminal from the sleep state. After waking up, the mobile terminal reads the paging message(s) transmitted in a downlink paging channel(s). The mobile terminal either connects to the network or performs the task instructed by the network via the paging message(s).
Depending on the amount of activity and connectivity involved, the sleep mode can be categorized into two sub-modes as “idle (standby)” and “dormant”. In idle mode, the mobile terminal has no connection to the RAN; however, it is connected to the core network. In contrast, in the dormant state the mobile terminal is connected to the RAN. In order to assist mobility in sleep mode, the mobile terminal is registered in a registration area or “paging zone”. The mobile terminal informs the network of its location and status in the registration process. This enables efficient paging in case of network-initiated connection establishment. A registration area may be defined as a zone (e.g., one or more cells) respectively controlled by a base station (or Node-B) or a plurality of base stations (or Node-Bs). A registration area may be also be known as a “routing area”, “tracking area”, “location area”, or, for Universal Mobile Telecommunications Systems (UMTS) implementing 3G wireless communications, “UTRAN registration area (URA)”.
The mobile terminal performs a registration whenever the “registration area” is changed. In other words, whenever the cell the mobile terminal is camped on broadcasts a “registration area” identity which is different from the registration area that the mobile terminal previously registered, then the mobile terminal should perform a registration update. Here, it is assumed each cell broadcasts only one “registration area” identity. However, the registration area may be defined to include overlapping zones. In that case, the cell would broadcast multiple registration area IDs.
In the conventional paging procedure, two signals are used to convey the paging message. The first paging signal is used to indicate whether a paging message is being transmitted to a particular UE or group of UEs. The second paging signal carries the paging message(s) for the particular UE or group of UEs. The second paging signal is transmitted following the first paging signal at a fixed time offset from the first paging signal.
The mobile terminal uses Discontinuous Reception (DRX) in sleep mode in order to reduce power consumption. When DRX is used, the mobile terminal needs to monitor the first paging signal only at one paging occasion per DRX cycle. The length of the DRX cycle is core network domain specific and may be updated locally in the mobile terminal using information given in system information from the core network.
The core network usually knows when the mobile terminal will be monitoring the first paging signal within DRX cycle. Thus, if the network intends to page a particular mobile terminal, it sends the first paging signal at the time when the mobile terminal will monitor the paging channel. If the mobile terminal does not receive any paging in the first paging signal, it goes back to the sleep mode. Otherwise, the mobile terminal reads the second paging signal.
The network may page the mobile terminal to establish a network originated call or to trigger reading of updated system information. In response to the paging message, the mobile may establish a connection with the RAN (if the mobile terminal is in an “idle” state), or update the mobile terminal location using a cell update procedure (if the mobile terminal is in a “dormant” state).
Upon receipt of the paging response, the RAN knows the location of the mobile terminal at the cell level. Thus, the radio resources can efficiently be allocated to the mobile terminal for the call.
In the conventional system, the connection establishment and cell update response to a paging message (network-initiated connection) follow the same procedures as when the connection establishment/cell update is performed in response to a “terminal initiated connection”. In the latter case, the establishment cause is not known to the network until a connection request message is received by the mobile terminal. Therefore, the network can manage the connection setup only after receiving the initial connection request from the mobile terminal.